Please see these links will be benefit for you. 

Good luck

http://www.pnas.org/content/102/41/14503.short

http://www.sciencedirect.com/science/article/pii/S0925400505009986

http://link.springer.com/article/10.1007/s00542-005-0003-0

In most gas sensor applications, for gas detection, where heating is necessary to achieve max sensitivity: The heater element plays a major role.

1) Firstly the heater should be miniaturised, and should be a low watt heater, so as to minimise the power requirements to operate the sensor, when it is ultimately used for gas detection.

2) You gas sensing material should preferably give you maximum sensitivity at a low enough temperature, again this is useful to minimise your power requirements for operating the sensor.

3) Considering the above a small low watt heater just beneath the sensing element should serve purpose.

4) You are basically heating the sensing element, and not the surrounding, therefore a heater just underneath the sensing material must be designed.

5) If you try to heat the surrounding environment, and then expect your sensing material to reach the temperature, you are spending more elecrical power to operate your sensor. It will take more power and longer time to heat your sensor element. 

6) Moreover the environment around your sensing element may get modified/rarefied when you have a heated atmosphere, and can change the concentrationof the gas being detected or interacting finally with the sensor element.

7) you do get miniaturized cartridge type heaters from "element14" or RS components, or can make yourself with heater wire rapped on a mica sheet, or extract a miniaturised heater from a soldering iron.

8) Finally the aim in gas sensing, and the goal to be achieved is to detect an incoming gas at a certain low contentration using a sensing element which is heated to a very low temperature, or alternately no heating at all.

   Making a gas detector with no heating is a real challenge. You need to develop a real nice gas sensing material which change its properties under a detected gas, and reverts back to its original property when the detecting gas is removed.

K. Sreenivas 

Thanks Sir for your precious reply. Actually i made a gas chamber where the heater is arranged around the pad where i  will put my sample for sensing test. So can i know by which material should i make the pad which should sustain atleast 500 C temp and by which method i will get an electrical contact out of that for measurement.

Well you can always have a dome shaped glass chamber, which is placed on a metallic baseplate. which has holes in it and has vacuum feed throughs fitted into the base plate which can carry the electrical wires. from the inside of the chamber to outside.

1) Buy a simple cartridge heater, round shaped. and insert it in a hole made into a copper block.

   the wire of the heater can come out through the feed through hole.

Similarly you can insert a thermocouple into a thin hole in the metal block, and the thermocouple wires can come out through the feed through.

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In case you do not understand what is a vacuum feed through electrical contact.

Try to see if anyone has a thermal evaporation system used for thin film deposition. Such a system will have many feed throughs on its base plate.

One of my students developed a test chamber for gas sensing.

His name is Dr. Arijit Chowdhuri, he is on the research gate.  Hopefully he can send a nice picture of such a test chamber. 

Alternately I will also try to send a picture of such a simple test chamber.

Give me a couple of days.

Prof. K. Sreenivas